1. Field of the Invention
The present invention relates to mosaic recording devices.
2. Description of the Prior Art
Mosaic recording devices are known, as exemplified by German OS No. 2,527,647, which selectively eject recording liquid droplets, such as ink, onto a moving recording medium, such as paper, for punctiform representation of alphanumeric characters and images on the recording medium. Such mosaic recorders have a plurality of nozzles or jets arranged adjacent to one another in rows in a recording head for generating the individual points comprising the representation. The nozzles for such conventional devices have an inlet opening which is relatively large in comparison to the outlet opening, from which the droplet is ejected, with the nozzle tapering from the larger inlet opening to the smaller outlet opening. The inlet openings for the nozzles each have a piezoelectric transducer associated therewith which is movable by the application of a voltage of appropriate polarity thereto so as to effect ejection of a recording liquid droplet from selected ones of said nozzles in response to control signals for generating a character or image on the recording medium.
In recorders of the type described in German OS No. 2,527,647, the action of the piezoelectric transducer alone is not sufficient to eject a recording liquid droplet from the nozzle with sufficient speed to permit the liquid droplet to free itself from the surface adhesion of the opening of the nozzle in the recording head. The above-described tapered design of conventional nozzles, by virtue of laws of fluid mechanics known to those skilled in the art, increases the speed of the liquid droplet so as to impart sufficient energy to the droplet to overcome the surface adhesion upon exit from the nozzle. The factor by which the droplet speed is increased by passage through the nozzles is theoretically maximally equal to the ratio in size between the inlet opening and the outlet opening of the nozzle. In practice, however, the factor by which the droplet speed is increased will be less than the theoretical value as a result of energy losses due to, for example, turbulence of the liquid flow. Such energy losses are also influenced by the shape of the nozzles.
In conventional printers such as the device disclosed in German OS No. 2,527,647, the nozzles are generally conical and have a circular cross-section. The smaller exit opening has a diameter of approximately 50 micrometers in order to insure that a suitable droplet volume is obtained. The larger inlet opening in conventional devices has a diameter of at least 150 micrometers in order to obtain an increase in the ink flow speed by approximately a factor of 9. In order to obtain a clear printout, the nozzles must be disposed closely adjacent one another. It is desirable that the distance between each nozzle be approximately 250 micrometers, and therefore in conventional devices the relative crowding of the nozzles renders a nozzle structure having a suitable diameter of the inlet opening extremely difficult, if not impossible. Moreover, the piezoelectric transducers must be disposed very closely next to one another, because each transducer must cover the inlet opening of the nozzle associated therewith. Such a transducer structure is also difficult to realize in practice. The closely adjacent disposition of the nozzle inlet openings further results in interfering hydraulic coupling between the nozzles, which causes a significant reduction in the recording speed for obtaining a clear graphic presentation, that is, the chronological interval between the activation of two adjacent transducers must be extended.